1. Field of the Invention
This invention relates to the field of microwave filters and resonators.
2. Description of the Related Art
A microwave resonator is an electromagnetic circuit that can be tuned to pass energy at a specified resonant frequency. The resonator can be used in communication applications, either in space or on Earth, as a filter to remove unwanted frequencies from a signal outside of a bandpass frequency range.
The resonator comprises a structure that defines a cavity. The dimensions of the cavity determine the resonant frequency of the resonator. Any change in the dimensions of the cavity will cause a shift of the resonant frequency and a change in the bandpass characteristics of the resonator. Such a change may be caused by expansion or contraction due to thermal stresses, and will adversely affect the resonant frequency and bandwidth. To counteract this thermal effect, resonators typically employ some type of temperature compensating mechanism.
Temperature compensation for microwave resonators is conventionally accomplished by using a material that resists deformation under thermal stresses, such as a bimetallic material that deforms appropriately to temperature changes. Another known technique uses electrical compensators, such as dielectrics, to counteract the thermal effect.
A microwave resonator is provided that includes an external temperature compensating structure. The external microwave resonator is a cavity with a specified volume. The temperature compensating structure is configured and oriented relative to a wall of the microwave resonator. When the microwave resonator and the temperature compensating structure undergo thermally-induced deflection, the temperature compensating structure applies a restoring force to the wall of the microwave resonator. The applied force deflects the wall oppositely relative to the thermally-induced deflection so as to maintain the volume of the cavity, and thereby maintain the filtering characteristics of the resonator.
Another aspect of the invention provides a microwave resonator having a first body structure and a second body structure. The first body structure has a mating surface and a recess. The recess has a thinned end wall and an inner wall surface. The end wall and the mating surface are perpendicular to the inner wall surface and are located at opposite ends of the recess. The inner wall surface extends around the periphery of the recess and is centered on a central axis.
The second body structure also has a mating surface and a recess. The recess has a thinned end wall and an inner wall surface. The end wall and the mating surface are perpendicular to the inner wall surface and are located at opposite ends of the recess. The inner wall surface extends around the periphery of the recess and is centered on a central axis. The first and second body structures have abutting positions in which the mating surface of the first body structure abuts the mating surface of the second body structure and the central axes align. The recesses together define a cavity. The inner wall surfaces of the first and second body structure are configured to form an electrical continuity in the cavity. Importantly, the electrical continuity is maintained when the end wall of the first body structure is deflected.